1. Field of the Invention
The present invention relates to a positioning apparatus, an exposure apparatus, and a device manufacturing method, which are used in a process for manufacturing semiconductor devices and liquid crystal display devices.
2. Description of the Related Art
FIG. 8 is a view showing the arrangement of a positioning apparatus used in a conventional exposure apparatus.
Reference numeral 10 denotes a stage movable on a base; reference numeral 20, an actuator for positioning the stage 10; reference numeral 30, a driver for supplying current to the actuator 20; and reference numerals 401 and 402, electrical wires serving as current supply paths. Reference numeral 50 denotes a controller for performing servo control to position the stage 10 at a desired position.
The controller 50 outputs the target current value of the actuator 20 to the driver 30 based on a difference between the target position and positional information from a position detector (not shown) arranged on the stage 10. The driver 30 has a current control circuit (not shown) and controls operation so that a current output follows the input target current value.
The actuator 20 is classified into two types. The first type is a moving coil type, the motor coil portion of which is arranged in its stage 10, that is, a movable portion. The second type is a moving magnet type, the motor coil portion of which is arranged in a stationary portion, and which has a stage 10 that includes a magnet portion and does not receive current. In the moving coil type, electrical wires 401 and 402 connect the movable and stationary portions. For example, in FIG. 8, the electric wire 401 is a stationary electrical wire, while the electrical wire 402 connects the movable portion and the stationary electrical wire 401. The electrical wire 402 is bent or slid upon movement of the movable portion.
When an abnormality has occurred in servo control of the controller 50 for the stage 10, the stage 10 must stop urgently. If it is impossible to interrupt the servo control, a braking circuit 60 must apply a brake to the stage 10 using a non-servo control system. It is a common practice to employ a technique for applying a braking force to the stage 10 by generating a motor coil current which serves as a braking force of the stage 10 upon short-circuiting of the motor coil. This braking circuit 60 is a high-voltage, large-current circuit, resulting in a large circuit board. In either the moving coil scheme or the moving magnet scheme, the braking circuit 60 is often arranged in the stationary portion.
The electrical wires 401 and 402 may break due to degradation over time, and operation errors may arise in a maintenance operation. Particularly, the movable wiring portion of the moving coil motor is susceptible to degradation in strength due to repeated sliding and bending. The actuator 20 often has a plurality of motor coils for an increase in thrust and the number of axes. When one of the plurality of electrical wires or the electrical wires partially break, the braking force of the motor lowers.
In addition, if the electrical wire between the braking circuit 60 and the motor coil portion breaks, a braking current, generated by a counter-electromotive force upon short-circuiting of the coil, does not flow. As a result, the braking force lowers.
When the stage braking force lowers to increase a braking distance upon occurrence of an abnormality, the stage 10 may contact a neighboring structure at a high probability, and this leads to damage to the components in the neighboring structure and the stage 10.
There are available a scheme (see Japanese Patent Laid-Open No. 2000-16199) for detecting a break by inserting a break detection line in the outer shell of the electrical wire portion that is most likely to contact the neighboring structure and break, and a scheme (Japanese Patent Laid-Open No. 2006-318698) using a break prediction signal line more susceptible to a break than the neighboring electrical wires. It is, however, difficult to specify that specific portion of the movable wiring portion that sustains repeating bending and sliding, on which a largest stress load acts. It is not always the case that the detection line breaks first.